fix: handle empty AI500 coin list gracefully instead of error

kernel/engine.go

@@ -447,6 +447,7 @@ func (e *StrategyEngine) GetCandidateCoins() ([]CandidateCoin, error) {
 		if err != nil {
 			return nil, err
 		}
+		// 空列表是正常情况，直接返回
 		return e.filterExcludedCoins(coins), nil
 
 	case "oi_top":
@@ -466,6 +467,7 @@ func (e *StrategyEngine) GetCandidateCoins() ([]CandidateCoin, error) {
 		if err != nil {
 			return nil, err
 		}
+		// 空列表是正常情况，直接返回
 		return e.filterExcludedCoins(coins), nil
 
 	case "mixed":

provider/nofxos/ai500.go

@@ -73,8 +73,10 @@ func (c *Client) fetchAI500() ([]CoinData, error) {
 		return nil, fmt.Errorf("API returned failure status")
 	}
 
+	// 空列表是正常情况，不是错误
 	if len(response.Data.Coins) == 0 {
-		return nil, fmt.Errorf("coin list is empty")
+		log.Printf("ℹ️  AI500 returned empty coin list (no coins meet criteria currently)")
+		return []CoinData{}, nil
 	}
 
 	// Set IsAvailable flag

trader/auto_trader.go

@@ -534,6 +534,12 @@ func (at *AutoTrader) runCycle() error {
 		return fmt.Errorf("failed to build trading context: %w", err)
 	}
 
+	// 如果没有候选币种，友好提示并跳过本周期
+	if len(ctx.CandidateCoins) == 0 {
+		logger.Infof("ℹ️  No candidate coins available, skipping this cycle")
+		return nil
+	}
+
 	// Save equity snapshot independently (decoupled from AI decision, used for drawing profit curve)
 	at.saveEquitySnapshot(ctx)